My, how the doctor has changed in the last 50 years! Fans of "Doctor Who" know, of course, that the space-and-time-traveling doctor can regenerate his body when he needs to, which was a boon for the casting process that has allowed the classic British sci-fi series to continue for five decades with a changing lineup of actors in the titular role. There have been 11 official Whos since the BBC drama premiered on November 23, 1963, and in honor of this, the show's 50th anniversary year, here's our guide to who's who among Whos. — Kimberly Potts, Yahoo! TV